Study finds new explanation for the accumulation of organic compounds in oxygen-depleted marine areas
UNIVERSITY OF OLDENBURG
The Black Sea is an unusual body of water: below a depth of 150 metres the dissolved oxygen concentration sinks to around zero, meaning that higher life forms such as plants and animals cannot exist in these areas. At the same time, this semi-enclosed sea stores comparatively large amounts of organic carbon. A team of researchers led by Dr Gonzalo V. Gomez-Saez and Dr Jutta Niggemann from the University of Oldenburg’s Institute for Chemistry and Biology of the Marine Environment (ICBM) has now presented a new hypothesis as to why organic compounds accumulate in the depths of the Black Sea – and other oxygen-depleted waters in the scientific journal Science Advances.
The researchers posit that reactions with hydrogen sulfide play an important role in stabilizing carbon compounds. “This mechanism apparently contributes to the fact that there is more than twice as much organic carbon in the waters of the Black Sea as in oxygen-rich marine areas,” says Niggemann. “This provides a negative feedback in the climate system that could counteract global warming over geological periods.”
In the Black Sea, which covers an area almost twice the size of France, conditions rarely found in other marine regions have prevailed for around 7,000 years: stable stratification largely prevents the mixing of surface and deep waters. The water in the upper 150 metres is low in salt and oxygen-rich, and comes mainly from rivers like the Danube. Below that, there is a layer of higher density saline water that flows into the Black Sea from the Mediterranean via the Bosporus.
“When you open a water sample from the deeper areas of the Black Sea, the smell of rotten eggs almost knocks you over,” Niggemann says. On the surface, however, there is no indication that the Black Sea is a stagnant body of water in which, due to the lack of oxygen, bacteria produce foul-smelling hydrogen sulfide.Hydrogen sulfide reacts with dissolved organic matter
As the new study shows, this highly reactive molecule binds with substances from a diverse group of carbonaceous materials that are present in every litre of seawater. These substances are known as dissolved organic matter (DOM) – a complex mixture of countless different molecules that are the product of decomposed organic matter or bacterial metabolic processes.
“We were able to show very clearly that hydrogen sulfide reacts with the extremely diluted organic matter directly in the water,” Niggemann explains. The products of the reaction are potentially more durable than the starting materials and therefore accumulate in the water.
The team compared water samples from different locations in the Black Sea and other seas and rivers. Using various analytical methods, including the ultrahigh resolution mass spectrometer of the Marine Geochemistry research group at the University of Oldenburg, the researchers were able to characterize the dissolved organic matter in detail.
They found that almost a fifth of the organic molecules in the anoxic areas of the Black Sea contained sulfur – significantly more than in other seas. In addition, the team was able to establish that a high proportion of these compounds are only found in these areas, leading the researchers to conclude that the sulfur compounds form there through chemical reactions in the sulfidic water.Negative feedback relevant on geological time scales
Given that huge amounts of carbon are stored in dissolved organic matter – the world’s oceans contain roughly as much dissolved organic carbon as there is CO2 in the Earth’s atmosphere – the results of this new study are also relevant for the climate. “The volume of ocean waters completely depleted of oxygen quadrupled between 1960 and 2010.
Consequently, this sulfur-based mechanism of carbon storage could influence the chemistry of the oceans in the future,” says Gomez-Saez, the lead author of the study. But this negative feedback is too weak to have a noticeable impact on climate change under the current conditions, he adds. In geological history, however, there have been several periods during which large areas of the oceans were oxygen-deficient. During these periods this effect could have contributed to long-term removal of carbon dioxide from the atmosphere.
The water samples from the Black Sea were taken during an expedition with the research vessel Maria S. Merian. In addition to the team from the ICBM, researchers from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) in Bremerhaven, the MARUM – Center for Marine Environmental Sciences of the University of Bremen, and the Max Planck Institute for Marine Microbiology in Bremen participated in the study.
###
Mmm, in marine aquaria sulphur compounds are used to reduce nutrients … no loss of oxygenation.
The Black Sea is rich in organic matter because the sewers of half a dozen former soviet bloc countries dead end there.
Nature takes a bigger dump than humans.
Nah it always was an organic soup tureen. We humans can’t crap much up on a global scale – even when you dont like their politics. Mind you we didn’t half mess up our rivers like the Thames, Rhine Rhone to name some touchy feely ones as well as Volga, Don and Danube
The Black Sea and the Caspian sit either side of one of the largest, and longest human exploited, near-surface [organic matter] petroleum seeps on Earth. Anaerobic life predates plant and animal life, and its waste products include oxygen and carbon dioxide necessary for aerobic life forms to exist. Not strange at all to discover anoxic environments on Earth support carbon life forms.
Since this has all been going on for billions of years, sounds like there isn’t a “tipping point” to worry about. Ditto for ocean “acidification.” And microplastics are carbon capture, not a problem.
May have been a wasted effort stopping all that acid rain, though.
Please tell me about this seep. I have explored for oil in the Black Sea,and the Caspian, and cant think of any seeps of any size between the two
Baku? There the oil is so near the surface it is pumped up by “nodding donkeys”.
Alastair, I envy your experience. Perhaps I used the term seep too loosely, bbut Disputin answers it for me.
Literally the first thing that pops up on an internet search
Baku: The first oil well in the world.
And I had this one linked:
Natural emissions of methane from geological seepage in Europe
…
[I remember thinking that the paper would be supressed since the ongoing narrative seems to be that cattle and dairy are the greatest sources of natural gas in Europe, so people should starve in order to stop it. They’d probably be annoyed to find that the source actually occured naturally. ]
Baku and other seeps in the area were reputed to be among the sources for naptha used as Greek fire. Modern Iran and Iraq should be included, of course. But Turkey, Georgia, Romania, Russia, and Ukraine produce oil around the Black Sea. Ancient descriptions are similar to the blog that I linked above, instead of “nodding donkey” pumps, petroleum and naptha were scooped up by hand.
Unfortunately, I’ve not seen these things myself. I have read about them, and seen some travelogues that included descriptions of the use of petroleum as pitch and fuel, among others, as well as medicines and spas, allegedly back to Persian times.
I don’t know how they stack up to La Brea in California, but the area seems to have much more near-surface oil, and, at either second or third in the world, be a much larger field.
Doesn’t it seem obvious to assume that much of the anaerobic biology found in the subject Black Sea study has been feeding (evolved to) on the biological petroleum material and sulphur from that geology for a very long time?
A linguistic aside. The Black Sea was known to the Greeks as euxeinos Pontos “the hospitable Sea” . The Black Sea, due to restricted circulation is anoxic at depth ,and so an anoxic
Environment is known as a Euxinic environment.
Only geochemists could consider anoxic and hospitable to be synonyms
Or Greeks. They called the Furys the “Kindly Ones”!
Perhaps sailors would also consider the Black easier to navigate and sail than the Med. Or maybe, for Greeks, there were fewer hostile neighbors living and sailing around in it.
The Greeks probably didn’t know anything about the anoxic region below 150 meters.
i cant see anything new in this research and we have always looked for oil source rocks in the anoxic waters of restricted basins. In the anoxic environment any Sulphur around gets absorbed along with the organic carbon. that is why many crude oils are high in Sulphur content
Environmentalists have finally discovered the euxinic basins, only 100 years after petroleum geologists did.
Here’s a link to the original research article.
https://advances.sciencemag.org/content/7/25/eabf6199/tab-article-info
There could be some interesting things in it.
What’s not to like? For current health fad trendies, H2S is rotten egg gas and it is a VERY STRONG anti-oxidant.
More seriously, sulphur plays a part in plant nutrition that has long been placed in importance below Nitrogen, Phosphorus and Potassium nutrients. To the extent that this study helps that context, it should be welcomed.as advancing scientific knowledge. Geoff S
“Almost a fifth of the organic molecules in the anoxic areas of the Black Sea contained sulfur.” But they wanted to remain anonymous. I love Science.
>>The volume of ocean waters completely depleted of oxygen quadrupled between 1960 and 2010.<< an interesting claim. I’d have like to have seen a link on this one. Or are we just making this up?
Quote:”The volume of ocean waters completely depleted of oxygen quadrupled between 1960 and 2010″
<twitches eyebrow> <Utters: fascinating>
OKaaaaay, What was the start point of this ‘volume‘ – One litre or a Several Squigga Sverdrups?
<Enquiring mind> Where did the sulphur come from – is that not relevant?
Let me guess. Me me me me, I know the answer:
‘Twas a Climate Fixing Experiment that the dinosaurs attempted.
Mmmmmm, didn’t pan out too good for them did it?
Quote:”This mechanism apparently contributes to the fact that there is more than twice as much organic carbon in the waters”
sigh. You’re nor any sort of gardener, farmer or horticulturist are you.
Welcome to anaerobic decomposition, as happens in peat bogs – the refurbishment of same will. seemingly, Save The World.
According La Familia Johnson et al and Hangers On, here in the UK
Hello hello – ever heard of High Sulphur Coal (diesel/petrol).
Now all banned but where did that sulphur come from?
What you’ve found is an underwater peat bog, in the process of forming coal oil & natural gas.
I suggest you leave it alone or Princess Nut Nuts will have your balls in a similar vice as she has Boris’ in.
Quote:”the smell of rotten eggs almost knocks you over,” Niggemann says”
Gotta admit, you seem to have a Fairy Godmother looking after you.
When that smell gets any stronger, you actually lose your sense of smell.
Also lose your sense of conciousness, breathing, heart-beating and all brain & nervous function.
Permanently.
Hence why, here in the UK, it is utterly verboten to put old ‘plasterboard’ into landfill sites.
The Gypsum in it breaks down to H2S – really rather the last thing anyone needs when a new housing estate has been planted on the (full) landfill some years later
From section on Hydrochemical Conditions. “These conditions were first determined by Lebedintsev (1892)…..” Caspers, H. 1957. Black Sea and Sea of Azov. Chap 25, pp. 801-890, In, J. W. Hedgpeth (Ed.) Treatise on Marine Ecology and Paleoecology. I. Ecology. Memoir Geological Society America. 67. Covers geological history with a number of studies in the 1920s, 30s including organic matter and good old Desulfovibrio.